Semiconductor substrates called silicon-on-insulator (SOI substrate) have been developed instead of silicon wafers manufactured by thinly slicing ingots of single crystal semiconductors, and the semiconductor substrates each have a thin single crystal semiconductor layer over a substrate having an insulating surface. By using an SOI substrate, parasitic capacitance of a transistor can be reduced. If an integrated circuit is formed using such a transistor, it is said that it is effective for speeding up of operation and reduction of consumed electric power. Thus, application of SOI substrate to high-performance semiconductor devices such as a microprocessor has been expected.
As a method for manufacturing SOI substrates, a hydrogen ion implantation separation method is known (for example, see Reference 1: U.S. Pat. No. 6,372,609). The hydrogen ion implantation separation method is a method in which hydrogen ions are implanted into a silicon wafer to form a microbubble layer at a predetermined depth from the surface, the surface into which hydrogen ions are implanted is superposed on another silicon wafer, heat treatment is performed to cause separation using the microbubble layer as a cleavage plane, and a thin silicon layer (SOI layer) is bonded to the other silicon wafer. In this method, in addition to the heat treatment for separation of an SOI layer, which is a surface layer, it is necessary to perform heat treatment in an oxidation atmosphere to form an oxide film on the SOI layer, remove the oxide film, perform heat treatment at 1000° C. to 1300° C. in a reducing atmosphere to increase bonding strength, and recover a damaged layer on the surface of the SOI layer.
On the other hand, a semiconductor device in which a single crystal silicon layer is provided for an insulating substrate using a high heat-resistance glass is disclosed (Reference 2: Japanese Patent Published Application No. H11-163363). The semiconductor device has a structure in which the entire surface of a substrate made of a crystalline glass having a strain point of 750° C. or higher is protected with an insulating silicon film, and a single crystal silicon layer obtained by a hydrogen ion implantation separation method is bonded to the insulating silicon film.